Page 197 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Effect of Gas Wettability on Capillaries CHAPTER 5 181

Based on the water-displacing-gas in single-straight capillary experiment in this
chapter, the surfaces treated with gas-wetting alteration agent solution of 0%,
0.2%, and 8% concentrations, have nongas-wettability, neutral gas wettability,
and preferential wettability, respectively. The gas-wetting alteration agent solu-
tions with these three kinds of concentrations were used to process an etched
glass network model, and water-displacing-gas experiments were conducted on
the models with different gas wettability, to study the effect of gas wettability
on the percolation characteristic and distribution of gas/water system.

5.2.2.1 EFFECT OF GAS WETTABILITY ON GAS/WATER PERCOLATION
STATUS
Nongas-wettability model: In nongas-wettability (water-wet) model, serious
spontaneous capillary imbibition occurs as soon as water enters the model
slot, and the end of the model along the pore wall. Gas displacement by water
is nonpiston type. Whether channels or pores, water enters preferential along
the pore walls. In the water-displacing-gas front, the gas/water interface is an
obvious meniscus and water presents concavity as shown in Fig. 5.14A.
Neutral-gas-wettability model: From Fig. 5.14B, it can be seen that in the
neutral-gas-wettability model, water advances evenly in the pore channel, the
gas is displaced through piston and is more complete. The water/gas interface
in the displacing front is a plane, and the capillary force is zero.

Preferential-gas-wettability model: From Fig. 5.14C, it can be seen that in the
preferential-gas-wetting model, water moves along the center of the channels
all the time and enters the pores at the crossing. The displacing front presents
meniscus and water presents convexity. It is observed that a layer of gas film
adheres to the side walls of the channels.

(A) (B)

(C)
FIGURE 5.14
Effect of gas wettability effect on the gas/water seepage state. (A) Nongas-wetting, (B) neutral-gas-wetting, and (C) preferential-
gas-wetting.